The objective of this research project is to define the mechanism of catechol formation from aromatic chemicals in mammalian liver cells and to determine the role of catechole metabolites in toxicity. The chemicals to be studied are benzend, naphthalene, biphenyl, 4-chlorobiphenyl, chlorobenzene, bromobenzene, and 5,5-diphenylhydantoin. These chemicals are known to be converted to catechol metabolites in mammalian systems. Whether these catechols are formed by two, independent hydroxylations or by dehydrogention of an intermediate dihydrodiol metabolite will be determined. Isolate hepatocytes will be used for these studies and the incorporation into the catechol metabolite of 180 from 1802 and H2180 will be measured by mass spectrometry. The activity of the enzymes involved in catechol formation will be manipulated in isolated hapatocytes by the use of enzyme inhibitors and inducers in order to determine if these modifications alter the mechanism of catechol formation or alternatively, if the mechanism is entirely dependent upon the structure of the chemical. From these studies, an increased knowledge of factors which conatrol catechol formation will results. An understanding of catechol formation is important to toxicology because of the reactive metabolites which can be formed from catechols by further oxidative reactions i.e.o-quinones and semiquinoes. In the present research project, the role of chlorocatechol and bromocatechol in the hepatotoxicity of chlorobenzene and bromobenzene, respectively, will be investigaged. In addition the role of catechols in the covalent binding to protein of metabilites of benzene, naphthalene, biphenyl, 4-chlorobiphenyl, and 5,5-diphenylhydantoin will be investigated. These studies will be done with isolated hepatocytes as a model system. The protocols to be used will be designed from the extensive studies on catechol formation with hepatocytes from different species, sexes, etc. which will be conducted as a part of the metabolic mechanism studies. Since only a small number of catechol structures have been previously examined for their toxic protential, our studies will be very significant in evaluating the general toxic significance of metabolism of an aromatic chemical via the catechol/quinone/semiquinone pathway.